Objectives: Nowadays, the extended ecological plaque hypothesis equates dental health with the occurrence of acidogenic generalists in the plaque flora and explains disease-the irreversible demineralization of the dental hard tissue-by an ecologic shift in plaque composition, favoring acidogenic and aciduric specialists, following repeated conditions of high sugar. In the present study, aspects of the extended ecological plaque hypothesis were examined in retrospect. Method and Materials: Serving as a basis were data on (1) the caries incidence of children, classified according to their DMFT as having low or high caries risk; (2) the qualitative plaque composition of the children with the prevalence of mutans streptococci and actinomyces; (3) the amounts of acid and acid tolerance, determined by pH state titration (glucose), of representatively isolated strains of mutans streptococci and actinomyces; (4) the extrapolation of the acid amount to the occurrence of mutans streptococci and actinomyces in the plaque of children; and (5) the relationship between the extrapolated acid amount in plaque and caries incidence and the respective classification of the children into low and high caries risk. Results: The synoptic consideration of the numbers of A naeslundii and S mutans in plaque of children, with their capacity for acid production in vitro, reflected the caries risk classification. Conclusion: The analysis of the clinical, microbiologic, and in vitro findings concerning the virulence of the plaque isolates supports the extended ecological plaque hypothesis. Children with low caries risk had developed one new decayed surface within 4 years; children with high caries risk developed four within the same time period. Schlagwörter: acidogenic generalists, aciduric specialists, actinomyces, caries, mutans streptococci, plaque hypothesis